1. Field of the Invention
The present invention relates to a plasma heating device for heating a molten steel in a tundish, more particularly an anode system for the plasma heating device suitable for use in a tundish of a continuous casting apparatus.
The main object of the present invention is to provide such anode systems which are economical and simple in structure and can be used for a long period of time under severe service conditions.
2. Description of Prior Arts
For heating molten metal, such as molten steel in various metallurgical furnaces, the adoption of plasma heating has been becoming more and more common in recent years. In principle, the plasma heating device comprises a power source, a plasma torch (cathode) for generating a plasma arc, which makes an electrical path between the molten metal and the plasma torch and an electrode (anode) to supply current into the molten metal. Conventionally, the current supplying electrode (anode) is formed by placing electric conductive carbon bricks on the bottom surface of a stationary furnace, such as a melting furnace, and connecting a lead wire to the brick formation to provide a current path, or by forming part of the bottom portion of the furnace with a metal having a similar composition as the metal to be melted in the furnace instead of the bricks, and projecting part of the metal formation outside the furnace in the form of fins for necessary cooling. In the latter system, although the current supplying electrode is considerably melted by the molten metal, the molten metal pool remaining after the pouring of the molten metal from the furnace is allowed to solidify again prior to a subsequent charge of the furnace and this solidified metal can be used as part of the electrode.
However, in cases where the plasma heating is utilized for heating a molten metal in a tundish of a continuous casting apparatus as disclosed in German Pat. No. 1288760, the current supplying electrodes according to the above two systems have been confronted with the following problems.
In the case of the tundish of a continuous casting apparatus, as well known, it is necessary to strip off the solidified metal remaining on the bottom of the tundish after the pouring and during this removal operation, the electrode provided on the furnace bottom is very often damaged, and once damaged, must be replaced with a new one. Therefore, the service life of the current supplying electrodes according to the conventional systems are very short when used in the tundish. In addition, the tundish itself is more often replaced and the brick works are more frequently replaced as compared with the stationary furnaces, and each replacement of the tundish or the brick works requires renewal of the electrode, thus increasing the running cost of the tundish operation and complicating the over-all works including the tundish replacement and the brick works replacement.
Under such situations, an upper-insertion type of current supplying electrode has been proposed for the plasma heating usable in the tundish in a continuous cast in apparatus as disclosed in Japanese Laid-Open Patent Application No. Sho 59-107755. This type of anode, however, has technical and economical problems such that it is necessary to prevent the melting of the anode itself in order to increase the service life, and for this a precious material must be used. For these reasons, the proposed anode has not yet been commercially used with success.